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Troubleshooting a string of LED Christmas lights

Discussion in 'LEDs and Optoelectronics' started by Msadrakula, Dec 9, 2019.

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  1. Msadrakula


    Dec 9, 2019
    I have a couple of hundred feet of LED Christmas lights surrounding my outdoor deck. They are unusual in that there is a brick where they plug into 120 volt AC outlet that I assume is the AC to DC converter. The sets are strung together by joining a two conductor cylindrical connector that is on the end of the set. In the middle of this run I have about 10 bulbs on both sides of one of these junctions that are not lit. I have seen people trouble shooting these types of lights and they are always looking for a bad bulbs.

    Here is the problem. I have 200 feet of lights with about 10 ft in the middle that are dark. I randomly remove one of the working bulbs in the good section and it had no effect on the rest of the string Everything stayed lit before and after the dead section. This would lead me to believe that these bulbs are connected in parallel since removing one bulb did not kill the whole string. Also there are three wires along the whole string except for when you get to the end where the cylindrical connectors are only two wire connectors.

    So I convinced myself that it can't be a dead bulb since the good part of the string stays lit even if a bulb is removed. If I had a broken wire the bulbs should be out all the way to the end of the string. This has me stumped. Any insight would be appreciated.
  2. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    Probably a combination parallel-series.
    Some led lights put two bulbs in parallel with opposite polarity (anode/cathode) and work on half wave rectification. So light string won't go out unless both parallel leds go out.

    I would guess it is a bad led somewhere.
    You could pain stakingly check them all, or buy a battery operated light tester that finds the open circuit faster.
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